In conventional microwave ovens with a turning tray disposed in a cooking chamber of an oven case for uniform heating, ordinary electric motors, for instance, induction motors with reduction gear means, have been used for turning the tray. In such conventional ovens, the mechanism is complicated and expensive because of the use of a motor and the reduction gear means. Moreover, because a shaft for revolving the turning tray is disposed to penetrate the bottom of the cooking chamber, the floor plate has a shaft hole which permits boiled-over over juice to pass into the reduction gear means and the motor. Therefore, the conventional microwave oven is liable to have troubles resulting from rust on the mechanical parts and deterioration of insulation caused by the boiled over juice.
In order to overcome this shortcoming of the above-mentioned conventional microwave oven, there has been proposed a device comprising a first set of permanent magnets fixed under the turning tray and a second set of several permanent magnets fixed to a turning means situated underneath the floor plate of the cooking chamber in a manner such that the second set of the permanent magnets and the first set of the permanent magnets are magnetically coupled so as to interact with each other to drive the turning tray when the turning means revolves. Such improved apparatus still has the shortcoming of large bulk because of the use of a motor and a reduction gear means.